This invention relates to an ultrasonic horn for use in manufacturing operations such as bonding, perforation, and cutting.
Ultrasonic horns are used to distribute ultrasonic energy in a variety of industrial processes. One example involves bonding of two thermoplastic sheets of material together in the manufacture of personal care products such as diapers.
Ultrasonic horn assemblies can have a number of distinct components, which can be connected in a stack. In one arrangement, these components may include a power excitation device known as a converter (or driver assembly), amplitude modification devices known as boosters, and an ultrasonically energized tool known as an ultrasonic horn, which contacts a work piece.
Upon energization ultrasonic horns cyclically expand and contract, which expansion and contraction is the driving force for the bonding or other mechanical operation performed by the horn. For example, a horn may expand and contracts a total amplitude of 0.003 inches (0.0075 cms) at a frequency of 20,000 Hz. This translates to a total movement of 120 inches (300 cms) of movement per second. This movement corresponds to an energy value applied to the work piece. Some of the energy is simply returned as elastic reaction, and most of the energy is dissipated as heat, which melts the two materials being bonded.
Generally, horns have been manufactured by machining a final horn shape from forged bar stock, such as titanium bar stock. Forging by its nature mechanically deforms grains, yielding a wrought horn microstructure. The alignment of deformed grains according to a wrought microstructure affects the natural cyclic bulk expansion and contraction of the horn as it is energized. In particular, the natural expansion and contraction of the horn is orthotropic or non-isotropic, that is, it is not uniform in all directions, and is preferential in one or more directions. The expansion and contraction in various directions is affected by the directional alignment of grains in the microstructure. The resulting non-uniform expansion and contraction of the horn is referred to as a coupled three-lobe breathing mode.
Inasmuch as a forged horn expands and contracts non-uniformly, the degree of expansion and contraction perpendicular to the work piece, which is the direction of work performed on the work piece, varies slightly depending on how the grains are aligned with respect to the work piece at the instant work is performed. As such, there are radial directions of maximum expansion and contraction, radial directions of minimum expansion and contraction, and radial directions of intermediate expansion and contraction. With ultrasonic rotary horns, the horn is continually rotating, such that some products are bonded with the horn in a rotary position of maximum expansion and contraction, other products are bonded with the horn in a rotary position of minimum expansion and contraction, and other products are bonded with the horn in a rotary position of intermediate expansion and contraction. The amount of energy transferred to respective work pieces therefore varies, and non-uniform bonding or other work can result.
Rotary horn resonant operating frequency is largely dependent on the outside diameter of the horn. As the outside diameter is reduced, the resonant frequency increases. Not all forged horns of the same diameter have the same resonant operating frequency, because resonant operating frequency is also largely dependent on the microstructure of the horn. And because wrought microstructures vary substantially in terms of grain size and grain alignment from one forging to the next, there is a corresponding variance from one forging to the next in terms of resonant frequency, even for forgings of the same diameter. As such, just because a first forging of a given diameter is determined to have a resonant operating frequency of 20,000 Hz does not mean that a second forging of the same diameter will also have a resonant operating frequency of 20,000 Hz. This is especially true of forgings from distinct billets having distinct microstructures. Each forging must be separately tuned to the desired frequency. In order to tune a horn to, for example, 20,000 Hz, one practice has been to produce the horn slightly oversized and then machine the diameter progressively smaller until the frequency of 20,000 Hz is achieved.
In response to the above difficulties and problems, the invention provides an ultrasonic horn which has isotropic expansion and contraction characteristics upon ultrasonic excitation, and which uniformly applies energy to successive work pieces. The invention also provides an ultrasonic horn for which the need for tuning is substantially reduced or eliminated.
Briefly, therefore, the invention is directed to an ultrasonic rotary horn for transporting ultrasonic energy to an operating location to apply the ultrasonic energy to at least one article at the operating location. The horn has a shaped metal horn body having a radial energy transfer surface and a central axis, wherein the horn body has substantially uniformly isotropic radial expansion and contraction amplitude upon excitation at a frequency.
In another aspect the invention is an ultrasonic horn for transporting ultrasonic energy to an operating location to apply the ultrasonic energy to at least one article at the operating location, the horn comprising a horn body having an energy transfer surface, wherein the horn body has a microstructure characterized by isotropically random directional grain alignment.
The invention is also directed to a method for manufacturing an ultrasonic horn for transporting ultrasonic energy to an operating location to apply the ultrasonic energy to at least one article at the operating location. The the method comprises forming metal powder into a horn body preform; and hot isostatically pressing the horn body preform to consolidate the metal powder to form a shaped metal horn body having central axis and a uniform isotropic microstructure characterized by randomly isotropic directional grain alignment such that the horn body has a uniformly isotropic radial expansion and contraction amplitude upon excitation at an operating frequency.
Other features and advantages will be in part apparent and in part pointed out hereinafter.